黑料网 study uncovers crucial function of a yeast enzyme Set2 whose well-conserved human counterpart is often mutated in cancers, especially kidney cancer.
黑料网 researchers have cracked a long-standing mystery about an important enzyme found in virtually all organisms other than bacteria. The basic science finding may have implications for understanding cancer development and how to halt it.
Researchers have known that the enzyme Set2 is important for transcribing genes 鈥� the process of making strands of RNA from the DNA. Transcription is critical for making proteins and other functional molecules. But Set2鈥檚 precise role in transcription hasn鈥檛 been clear. Now, 黑料网 scientists discovered that the enzyme is particularly important for keeping transcription working properly when cells are under stress. Without Set2, cells that become stressed through the lack of nutrients begin mis-transcribing genes in a way that prevents cells from adapting properly to the stress.
鈥淲e think this solves a mystery about the purpose of Set2, and we now understand much better how gene transcription is prevented from happening at the wrong place and time,鈥� said study senior author professor of biochemistry and biophysics and member of the 黑料网 Lineberger Comprehensive Cancer Center.
Set2 enzymes in yeast and other lower organisms have close relatives in all animal species and plants. Its human cousin SETD2 is often found mutated in cancerous cells.
鈥淭hese fundamental findings may help explain how SETD2 mutations could lead to inappropriate transcription within genes, which might then promote cancer initiation or progression,鈥� Strahl said. His team鈥檚 research on SETD2 is ongoing.
The research, published in Cell Reports, involved collaboration between Strahl鈥檚 laboratory and that of Ian J. Davis, MD, PhD, associate professor of pediatrics and genetics at the 黑料网 and member of the 黑料网 Lineberger Comprehensive Cancer Center.
This methyl-attaching process is called methylation. Research has shown in recent years that the particular histone methylation performed by Set2 serves as a quality control check on gene transcription.The discovery comes 15 years after the first studies of Set2 by Strahl and others, who found that the enzyme works by attaching molecules known as methyl groups to a support protein 鈥� or histone 鈥� around which DNA is spooled.
Transcription of a gene should start at a precise spot at the beginning of a gene and then continue until the end in order to fully transcribe the RNA. But in the absence of histone methylation laid down by Set2, transcription begins at the wrong places in the middle of a gene instead of at the beginning. If that is allowed to happen, the production of 鈥渃ryptic鈥� RNA transcripts can then interfere with the normal expression of a gene. The mis-expression of our genetic material can result in diseases such as cancer.
Strahl鈥檚 team thought Set2 might have something to do with these cryptic transcripts arising during stress. Previously, it was shown that Set2鈥檚 histone-methylating activity has the effect of attracting another enzyme to clear away chemical tags in the middle of a gene that, otherwise, can lead to inappropriate new transcription from within that gene.
鈥淏ut under typical laboratory conditions, the deletion of Set2 and the subsequent increase in cryptic transcripts didn鈥檛 seem to harm cells very much,鈥� Strahl said.
Strahl鈥檚 team then thought about cells under stress, which is what cells are like in disease states. His team conducted experiments to observe what happens in cells that don鈥檛 have Set2 when vital nutrients are removed. In this stressed state, cells normally activate a complex set of gene expression programs to help cope with the reduced nutrient resources.
鈥淣utrient depletion more accurately mimics what yeast cells experience in the wild,鈥� Strahl said.
The scientists examined yeast cells that were deprived of nutrients, or were exposed to chemicals that reliably trigger the low-nutrient response. In these cells, not having Set2 proved to have major consequences.
鈥淲e found that this inappropriate transcription at the wrong place in genes exploded to high levels in stressed cells, and often interfered with the normal genes,鈥� Strahl said. 鈥淎s a result, the normal changes in genes that help cells survive under low-nutrient conditions did not happen correctly, and the cells became extremely sick.鈥�
To Strahl and colleagues, the finding suggests that Set2 evolved to guard against harmful abnormal transcription in times of stress, when cells seem particularly vulnerable to this type of error. Why would cells be so vulnerable to cryptic transcription during the nutrient stress response? Strahl isn鈥檛 sure. But his team suspects that when there鈥檚 a sudden and widespread rearrangement of the molecular machinery of gene transcription, genes across the genome are left relatively open to inappropriate transcription.
鈥淲e found that a lot of the genes that show this crazy jump in cryptic transcription were not even related to the nutrient stress response,鈥� Strahl said. 鈥淚t鈥檚 as if there are genes throughout the genome that are just predisposed to this error, especially at this time when transcription is shifting dramatically.鈥�
Strahl and Davis and their colleagues plan further research to determine why cryptic transcription rises so dramatically during nutrient stress. They also intend to find out whether Set2 is important for safeguarding transcription during other types of cellular stress.
In addition, the scientists are now studying Set2鈥檚 human counterpart, SETD2, which for unknown reasons is often mutated in tumor cells, especially in kidney cancers.
鈥淚t鈥檚 possible that SETD2 normally works as a major tumor suppressor by preventing inappropriate transcription,鈥� Strahl said.
The lead author of the study was Stephen L. McDaniel, PhD, a former graduate student in the Strahl Laboratory. Other co-authors were Austin Hepperla, Jie Huang, Raghuvar Dronamraju, PhD, Alexander T. Adams, and Vidyadhar G. Kulkarni, PhD.
The National Institutes of Health funded this work.
Courtsey of Mark Derewicz and 黑料网 Health Care News Room.